Fan construction



March 14, 1961 c, cu

FAN CONSTRUCTION 2 Sheets-Sheet 1 Filed Oct. 21, 195"! g INVENTOR fiedfam? ATTORNEYS.

March 14, 1961 Filed 001:. 21, 1957 c. F. CULP 2,974,728

FAN CONSTRUCTION 2 Sheets-Sheet 2 INVENTOR' fiwm Wam- ATTORNEYS.

United States PatentO FAN CONSTRUCTION Chester F. Culp, Marshalltown, Iowa, assignor to Lennox Industries, Inc., a corporation of Iowa Filed Oct. 21, 1957, Ser. No. 691,428 3'-Claims. (Cl. 17 159) This invention relates generally to a fan construction,

and more particularly to a novel form of fan blade for use with an axial flow fan. In the commercial manufacture of fan constructions for use in the movement of large volumes of air at semi-pressures, as for example in crop driers and the like, it is highly important to achieve a low cost construction capable of achieving high operating efficiency for a given power input despite substantial flow resistance and operating semipressures, while maintaining blade stability and reliability. For the full achievementof these purposes, it is essential in such fan constructions to maintain a substantially constant blade pitch during fan operation, and to maintain such pitch stability throughout the lifetime of the fan. The elimination of such adverse characteristics as blade flattening and tip flutter during operation has long been recognized as a highly important objective in fan design.

It is therefore, a primary object of this invention to provide a fan construction having a plurality of blades particularly formed and contoured so as to maintain pitch stability during operation.

It is another object of this invention to providea fan construction having a plurality of die-formed blades particularly contoured so as to provide pre-stress forces within the blades for counteracting any tendency of the blades to distort or flutter during operation.

It is another object of this invention to'provide a fan construction having a plurality of fan blades characterized by the center of gravity points of successively radially outward blade sections from rootto tip lying in the same'radial plane but in successively forwardly disposed transverse hub planes.

It is still another object of this invention to provide a fan construction having a plurality of blades characterized by a forward rake at the tip of the fan blades for effecting convergent discharge flow towarda forward point on the projected hub axis.

Further object's and advantages of this invention will become apparent as the following description proceeds, and the features of novelty which characterize this invention will be pointed out with particularity in the claims annexed to and forming part of this specification.

A preferred embodiment of the invention is shown in the accompanying drawing, in which:

Figure 1 is a plan view of a fan construction embody- 7 ing the features and principles of the present invention,

as seen from the upstream flow. side;

Figure 2 is a fragmentary end elevational view taken in the direction indicated by the line 2-2 on Figure 1;

Figures 3 and. 4 are fragmentary elevational views taken substantially as indicated by the lines 33 and 4-4, respectively on Figure 1;

Figure 5 is a developed view corresponding to a planar pattern of one of the fan blades;

Figure 6 is an elevational 'view of one of the fan blades; and

V Figure 7 is a series of cross sectional views taken ice through the blade of Figure 6 at a successive series of plane from blade root to tip stations, designated by the lines a-a to e-e, each plane being normal to a radial reference plane R-1 shown in Figure 6.

Referring now more particularly to Figure 1 of the drawing, I have indicated generally at 10 a fan construction embodying the principles and features of the present invention. A central hub 12 is provided for mounting upon a suitably driven rotary shaft, the direction operating rotation being indicated by the arrow. The hub 12 provides an outermost peripheral flange 14 of generally cylindrical shape. A plurality of peripherally equi-distantly spaced blades 16 are mounted upon and secured to the hub flange 14 in radially outwardly extending relation. The fan blades 16 may be secured to the hub flange 14 by welding, and each blade may be p'rovided with a reinforcement pad 18 at its downstream or discharge surface (see Figures 2 and 3) to insure stable attachment and rigidity of the blades at their root connections.

In Figure 5 of the drawing, I have indicated one of the blades 16 as a developed view, in the form of a flat sheet pattern 16', without the surface curvatures or contours which characterize the present invention. The blade, in both developed and final contoured form, provides a leading edge 20, a trailing edge 22, a root 24, and a tip 26. It. will be noted from the pattern of Figure 5 that the leading edge 20 lies along a straight line.

The surface curvatures of the blade 16 in its final contoured form are best revealed by a series of successive cross-sections taken at various stations along the length of the blade of Figure 6, and which have been arranged for comparison in Figure 7 of the drawing as sections a through e. The sections have been taken along successive parallel planes or stations from root to tip,

common radial plane CG (see Figure 6). I All section planes, normal to the radial reference/plane R1, will be referred to as sectional reference planes Sa through 8-2 (see Figures 3 and 6).

- The blade leading edge 20 lies within a single plane parallel to the radial reference plane R-l. As best seen in Figure 3 of the drawing, the leading edge 20 is curved from root to tip toward the downstream direction. The trailing edge '22, as seen in Figure 6, diverges away from'the leading edge 20 from root to tip. The trailing edge 22 also curves from root to tip away from the downstream direction, as seen in Figures 3 and 4. The line of maximum surface height of the blade sec 'tions has been indicated by the reference line R-3 in i blade sections a through e are raked forward at the leading edge 20. In addition, the various sections are characterized by being disposed at progressively more downstream locations from root to tip. In order to more clearly point out the progressive downstream curvature of the entire blade from root to tip, a transverse reference plane R-Z extending across the upstream end of the hub 12 v "has been designated in Figure 3. his apparent that the section plane S-e is disposed closer to the transverse reference plane R-2 than is the section taken at reference plane S-a. Successive radially outward sections along the blade length from root totip lie progressively more forwardly toward the downstream direction or direction a 3 of discharge flow. Thebladeatherefore, are characterized by the center of gravity points of successively radially outward sections from root to tip lying in the same radial plane but in successively forwardly disposed transverse planes.

As a "result of this unique bladefforr'riation, and particularly the forward rake of the leading edge at the blade tip, air is discharged in a downstream direction in a Convergent pattern toward 'a point lying substantially on the projected axis of fan rotation. This convergent direction of the air has been generally indicated by fiow arrows at the tip of the blade shown in Figure 3 of the drawing. This characteristic of air flow direction tends to fill up the projected volume downstream ofthe fan hub, thereby minimizing the tendency for low pressure zones to be established immediately forwardly of the fan hub, as in conventional fan structure. Such low pressure zones. result in turbulence at the blade roots, and often produce a reverse air flow about the hub periphery. Such effects are the result of the inherent inability of fan blades to achieve any significant air impelling by their surface areas from the root to stations at about two-thirds of the way toward the tip. Conventional blades, however, tend to direct the air from the effective 'impelling areas adjacent the blade tips in directions parallel to or divergent from the axis of rotation, and there is a marked tendency in prior blade structures to permit air to slip along the blade surface in a radial direction at the tip, resulting in substantial losses in impelling efficiency.

Blades contoured in the manner of the present invention achieve a substantial downstream air flow convergence, thereby resulting in substantially increased fan efficiency over prior known constructions. The particular blade contours disclosed provide the further advantage of introducing predetermined stresses within the blade to counteract and oppose the centrifugal force stresses during normal fan operation which tend to cause blade flattening and tip flutter in prior conventional structures. Such pre-stressed blades are capable of maintaining their contours during manufacture and particularly when the root portions are welded to a hub structure, thereby insuring even blade angles for all the blades about the periphery of a fan assembly. In order to achieve and maintain the blade contours of the present invention during manufacture, it is necessary that the blades be die-formed. In this way, close tolerances and high quality construction may be maintained.

Although Ihave herein shown and described certain preferred embodiments of my invention, manifestly it is capable of further modification and rearrangement without departing from the spirit and scopethereofQ I do not, therefore, wish to be understoodas limiting this invention to the precise embodiment herein disclosed," except as I may be so limited by the appended claims.

I claim:

1. A fan construction comprising a center hub having a longitudinal axis of rotation and a plurality of peripherally spaced blades extending radially outwardly from said hub, each of said blades being characterized by the center of gravity points of successively radially outward sections, taken in planes parallel to-the hub axis of rotation and at right angles to a radial reference plane, from root to tip lying in a common radial plane but in successively forwardly disposed transverse planes relative to the direction of discharge flow, and said sections of each blade being further characterized by a forward rake at the leading edge for effecting convergent discharge flow toward a forward point on the projected hub axis.

2. A fan construction comprising a center hub having a longitudinal axis of rotation and a plurality of peripherally spaced blades extending radially outwardly from said hub, each of said blades having a leading edge lying substantially in a plane parallel to a radial reference plane, each of said blades being characterized by the center of gravity points of successively radially outward sections, taken in planes parallel to the hub axis' of rotation and'atright angles to said leading edge plane, lying in a common radial plane which diverges away from said radial reference plane, said successive center of gravity points lying in successively forwardly diposed transverse planes relative to the direction of discharge flow, and said sections of each blade being further characterized by a forward rake at the leading edge for effecting convergent discharge fiow toward a forward point on the-projected hub axis.

3. A fan construction comprising a center hub having a longitudinal axis of rotation and a plurality of peripherally spaced blades'extending radially outwardly from said hub, each of said blades being characterized by the center of gravity points of successively radially'outward sections, taken in planes parallelto the hub axis of rotation and at right angles to a radial reference plane, from root to tip lying in a common radial plane but in successively forwardly disposed transverse planes relative to the direction of discharge flow, and said sections of each blade being further characterized by a forward rake at the leading edge for effecting convergent discharge flow toward a forward point on the projected hub axis, the leading edge of each blade lying substantially in a plane parallel to said radial reference plane and'being curved progressively forwardly from root to tip, whereby said blades'are particularly contoured so as to provide prestress forces for counteracting blade distortion forces during fan operation.

References Cited in the file of this patent UNITED STATES PATENTS 

